Takamasa Tsumurai 

Takamasa Tsumurai focuses on technology, data protection, advertising, and platform regulation.  His practice particularly centers on privacy and data governance, AI-related legal issues, open-source software (OSS) license compliance, online platform regulation, and commercial contracting.   

Prior to joining the firm, he served as in-house counsel at LY Corporation (formerly Yahoo Japan and LINE), where he advised on a broad range of legal matters across major web-based services, including online media platforms and digital advertising services. His experience includes contract review, privacy impact assessments (PIAs), and data governance support, with particular emphasis on compliance with Japan’s Personal Information Protection Act (APPI), AI- and machine-learning-related copyright and data usage issues, and OSS governance frameworks. 

Drawing on his background as a software engineer, Takamasa brings strong technical literacy and regularly works closely with engineers and product teams, enabling him to provide practical, implementation-oriented legal advice that bridges technology and law for both domestic and international clients. 

Practice Areas 

• Data Protection & Privacy (APPI) 

• Technology & Platform Services 

• AI & Machine Learning (Copyright, data governance, model training) 

• Open Source Software License Compliance / Governance 

• Advertising & Labeling (The Act against Unjustifiable Premiums and Misleading Representations) 

• Copyright & Digital Content 

Admissions

Japanese Bar (The Tokyo Bar Association)

Education 

• Kyoto University Law School (J.D.) 

• Kobe University, Faculty of Law (LL.B.) 

Professional Experience 

• Associate, Mori & Partners, 2026–present 

• Legal Counsel, LY Corporation (Yahoo Japan / LINE), 2022–2026 

• Media Legal Division (2022–2025) 
• Advertising & Data Legal Division (2025–2026) 
• Concurrent roles in Privacy Governance Team and OSPO Team (OSS Governance) 

• Engineer, IT Software Company, 2020–2021